OS X Mavericks Developer Preview 7

Apple Releases Developer Preview of OS X Mavericks With More Than 200 New Features
The next version of the Mac operating system, OS X 10.9, is officially labeled as OS X Mavericks. Mavericks, named after an epic surfing spot in northern California, has a lot of new features, but also represents a change in naming conventions away from the familiar cat themes. In future versions of OS X will follow the same naming convention and all be named after inspirational places throughout California, where Apple is located.

Installation
Network migration from earlier versions of OS X requires the Migration Update for Snow Leopard, Lion, or Mountain Lion, available from the Mac Dev Center.
Migration from Windows is not supported in Developer Preview 7.

iBooks
PDFs imported into iBooks in previous seeds of OS X Mavericks may be renamed when opened with Preview.

Other
Screen recordings taken with Developer Preview 7 are not compatible with earlier releases of OS X.
Fusion Drive volumes created with Developer Preview 7 are not compatible with OS X v10.8.4 or earlier.
Moving a full-screen Aperture window to a secondary display may prevent the app window from being visible in subsequent attempts to use full screen.
In Full Screen in Aperture, some menus and thumbnails aren’t immediately available until interacted with by the user.
When in Full Screen in Aperture, the toolbar at the top of the window may not be usable until it is locked.
Starting in Developer Preview 4